Rubber compositions which are expansible under vulcanization conditions have been known in the prior art for a long time. They are used predominantly in the construction of vehicle bodies and are intended to interconnect various parts of a vehicle body so as to fill the gaps therebetween. For this purpose, it is necessary that the inserted strips should expand to a considerable extent during the stoving of the lacquer and at the same time should unite satisfactorily with the surface. A further requirement is that the finished, expanded strips should have a low water-absorption capacity and should effect a rigid connection between the workpieces and should be resistant to under-rusting and thus do not cause corrosion.
The propellant gas hitherto used for these vulcanizing rubber compositions was usually nitrogen and carbon dioxide, with azobutyric acid dinitrile, azodicarbamite disulfohydrazides, sodium hydrogen carbonate, or, alternatively, dinitroso compounds being used as the gas-developing substances.
However, it has transpired that optimum results could not be obtained with the known propellant gas substances.